| Transition of shells | |||||
| plies | material | bearing edge | remarks | ||
| 1960's | 3 | Pearl finish | Mahogany Poplar Mahogany |
Round edge | White painted interior
（RESA-COTE） Reinforced Earlier 60's shells are Mahogany, Maple, Maple |
| Lacquer finish | Maple Poplar Mahogany |
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| 1970's | 3 | Mahogany Poplar Mahogany |
Clear lacquered interior （LUD-COTE） Reinforced |
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| Acryl | Vistalite series | ||||
| 1980's | 6 | Maple Cross-grained veneer |
Clear lacquered interior | ||
| Stainless steel | |||||
| Acryl | Vistalite series | ||||